An internal combustion engine, such as that which is typically deployed within a vehicle, respectively includes several cylinders into which air and fuel are selectively mixed. The air-fuel mixture is then ignited, effective to cause a piston to move and to impart torque upon a crankshaft, thereby allowing the vehicle to be driven.
In order to reduce the amount of undesirable emissions, in order to reduce undesirable vibration or "engine knocking", and in order to allow the engine to more efficiently utilize the fuel, it is desirable to cause the ratio of the contained air and fuel within each of the respective engine cylinders to substantially equal a certain value or to reside within a relatively narrow range of values.
This objective is typically achieved by estimating the amount of air which is contained within each of the cylinders, commonly referred to as "the air charge", and then, based upon these respective estimates, dynamically regulating or metering the amount of fuel which is operatively communicated into the respective cylinders. Conventionally, the air charge is estimated by use of only one of four known techniques or methodologies which respectively utilize the engine speed and throttle position; the engine speed and the pressure of the intake manifold; the engine speed and a measured flow rate of air entering the intake manifold; and the position of the throttle and the pressure which is resident within the intake manifold.
Each of these previously delineated techniques has certain undesirable and varying measurement inaccuracies. The use of only one of these four previously delineated techniques therefore produces air-charge estimates having varying degrees or amounts of inaccuracy, thereby preventing the attainment of the previously delineated and desired cylinder air-fuel ratio. The third previously delineated technique is also undesirable since it requires the use of a relatively costly flow meter, thereby further increasing overall vehicle costs and undesirably increasing the complexity of the engine assembly.
There is therefore a need for a cylinder air-charge estimation assembly and technique which overcomes at least some of the previously delineated drawbacks of prior air-charge estimation assemblies and techniques and which, more particularly, allows the air-fuel ratio of each of the engine cylinders to be made substantially and respectively equal to a certain desired value or to reside within a relatively narrow range of desired values as the engine is operated.